The invention relates to a thrust ring for use in bearing systems for bolts of a universal joint for use in cardan shafts and to a method for producing a thrust ring. It also relates to a bearing system for bearing a bolt of a universal joint in a bearing bore of an articulated yoke for use in cardan shafts. Finally, it relates to a cardan joint arrangement having a bearing system of this type.
Cardan joint arrangements, in particular the bearing systems for bearing bolts of a universal joint in articulated yokes for use in cardan shafts, are known in a wide variety of designs for a multiplicity of possible uses. To represent this prior art, reference is made to a publication Voith Forschung und Konstruktion [Voith Research and Design], Vol. 33 (1998), Article 10 xe2x80x9cEntwicklung wxc3xa4lzgelagerter Gelenkwellen fxc3xcr die Hauptantriebe schwerer Walzgerxc3xcstexe2x80x9d [Development of cardan shafts mounted on rolling bearings for the principal drives of heavy rolling stands], and to Voith-Druck G 1135, 11.91. These documents disclose designs of cardan joint arrangements for cardan shafts which comprise at least one universal joint which is mounted in at least one articulated yoke. The articulated yoke itself may be of single-part or two-part design. To attach the universal joint in the articulated yoke, a suitable bearing arrangement is provided for each individual bolt. The bearing arrangement comprises at least one radial bearing and an axial bearing. There are numerous possibilities for the arrangement of the axial bearing, although a suitable design of the individual elements of the bearing will emerge when account is taken of the deformation which occurs while the cardan shaft is operating. Article 10 from Voith Forschung und Konstruktion, Vol. 33, discloses a design with a radial/axial bearing in which the individual components of the bearing arrangement, the seals, the connection structure of the bearings and the flange connections which transmit the torque are carefully matched to one another with regard to stress distribution and deformation under load. In this design, the radial bearing comprises three rows of solid cylindrical rolls which are guided inside the inner ring. The radial bearing inner ring is supported, via a collar, on the bolt end sides. An outwardly facing collar at the other end of the ring forms the inner race of the axial bearing. In this design, the axial force is introduced via the bolt end side. In this arrangement, the materials of the individual elements are selected according to their different functions, i.e. high-strength heat-treated steel is selected for the drop-forged universal joint and rolled case-hardened steel is selected for the bearing sleeve. The problem of a bearing arrangement of this type is that the individual rolling bearings are exposed to high torque impacts and simultaneous transverse accelerations, in particular when used in rolling mill drives. The impact loads, with large and rapidly changing bending angles, cause elastic deformation of the articulated yokes both in the region of the flange and inside the yoke eye. The bore widens and generally adopts a non-circular shape.
However, the introduction of the peripheral force causes the most deformation at the universal joint. The direction of this force oscillates with the positive or negative value of the operating bending angle and also changes with each reversing operation. These operation-related and design-related influences result in alignment errors with an unfavorable introduction of loads into the bearing, namely a center offset of the yoke bore, a skew positioning of the bore, bending of the bolt and radial play in the rolling bearing and spring deflection of the rolling bearing. The result is an uneven radial pressure distribution in the bearing bore, resulting in the contact at the locations of contact of the rolling bodies of the radial bearing changing from linear to punctiform, and also leading to excessive edge stresses. The rolling bearing connection parts, universal joint and articulated yoke are therefore adapted to one another in terms of deformation travel. Since the axial bearings of heavy cardan joints are generally arranged in the region of the root of the bolt of the coupling, these influences which have been listed lead to tilting of the axial bearing races. In this context, the deformation of the bolt in the region of the root has the greatest influence, since this is where the curvature of the bending line related to the bending moment is greatest. This leads to high edge stresses in one segment of the axial bearing and to the rollers lifting off in the opposite segment, leading to a drastic reduction in the load-bearing capacity.
To allow a simple structural design of a radial/axial bearing unit of the cardan joint, therefore, the races of the bearing sleeve for both bearings have been centered and axially fixed over the lateral and end faces of the bolt. If the bolt then bends under a load, the bearing sleeve follows a tangent which touches the bending line of the end of the bolt. Therefore, plane parallelism is retained even when the universal joint is under load. A significant drawback of a design of this type, however, is that the design of the individual bearing element is relatively complicated and requires a large number of elements, in particular with regard to the design of the bearing cover. During the structural execution, and in particular designing, of the individual components, therefore, it is always necessary to take account of the deformation travel which may occur, so that it is impossible to provide a satisfactory design irrespective of knowledge of these influences.
In another solution for fitting the bearing arrangement known from EP 0 785 370 A1. In this arrangement, the inner ring of the radial bearing, in the fitted position, on the axially inner side, includes a collar which extends radially away from the axis of the bolt mounted in the articulated yoke. The term axial is understood as meaning a direction which runs substantially parallel to the axis of the bolt mounted in the articulated yoke, as seen from the joint axis. In this context, the term joint axis is understood as meaning the extended axis of the component connected to the articulated yoke. This axis extends through the intersection point, whether it is either direct or projected into a plane, of the bolt axes of the universal joint. The axes of the bolts, which are offset in each case by 90xc2x0 with respect to one another, may lie in a common plane or may be offset with respect to one another in mutually parallel planes.
The collar of the inner ring of the radial bearing at least indirectly forms the axially outer running surface of the axial bearing. This means that the collar may on the one hand directly form the running surface for the rollers or the rolling elements of the axial bearing designed in some other way, or on the other hand it is also possible for the running surface of the axial bearing, i.e. the outer ring of the axial bearing, as seen in the fitted position on the bolt, to be supported on this collar. In the fitted position, the outer ring of the radial bearing has, in the axial direction, an inner collar which extends radially toward the axis of the bolt mounted in the articulated yoke. The collar of the outer ring of the radial bearing at least indirectly forms the axially inner running surface of the axial bearing. The outer ring also has a so-called axially outer collar, as seen in the fitted position, which is assigned a stop in the yoke eye. Furthermore, the inner ring is assigned an axially outer collar, as seen in the fitted position, which is directed toward the axis of the bolt mounted in the articulated yoke and forms an axial stop for seating the inner ring in the end-side region of the bolt. This outer collar can be connected in a positive and/or nonpositive manner to the bolt mounted in the articulated yoke. This collar may be designed in such a manner that it forms a structural unit with the inner ring.
Another possibility is for the collar to be formed by a separate component. This separate component may, for example, be in the form of a cover. The cover is preferably designed such that at least a first part of its cover inner surface, which is understood as meaning that cover surface which faces toward the joint axis in the fitted position, bears on the end side of the bolt mounted in the articulated yoke, while a second part of its cover inner surface, in the fitted position, forms a stop for the inner ring of the radial bearing. Contrary to the rigid bearing structure which is otherwise desired, this design produces elastic attachment of the axial bearing. Overall, this type of elastic attachment leads to improved bearing properties of the individual bearings of the bearing system and therefore to a longer service life of the bearing units and also of the universal joint arrangement as a whole. However, a significant drawback of a design of this type is that it entails a considerable design and manufacturing outlay, since attaching the bolts to the articulated yoke halves requires a large number of components which are responsible for the functions which have been described. Therefore, providing a bearing arrangement of this type is also very expensive, in view of the need to adapt the individual elements to one another and to adapt the associated tolerances which have to be observed.
Furthermore, particularly in cardan joint arrangements for heavy cardan shafts, in which the bearing bore of the articulated yoke may be of closed design, i.e. is designed as a blind bore, and in which as well as the axial bearing arrangement the sealing components are also to be arranged in the region of the bolt root, the known solutions entail considerable design and manufacturing outlay, since attaching the bolts to the articulate yoke halves requires a large number of components which are responsible for the functions which have already been described for other designs.
Therefore, the invention is based on the object of further developing a bearing system for cardan joint arrangements of the type described in the introduction, in particular for use in heavy cardan shafts, to avoid the above-mentioned drawbacks, i.e. so that this system has a simple structure and a small number of components. It should be possible to completely or at least nearly completely eliminate the negative influences on the bearing arrangement, in particular the axial bearing, during deformation of the torque-transmitting components without knowledge of the specific load situations in use, with a solution which is standardized as far as possible. The cardan joint arrangement, in particular the bearing system and its individual elements, are to be distinguished by low design and manufacturing outlay and low costs.
According to the invention, an annular basic element is ground to form a thrust ring for use in an axial bearing in a bearing arrangement for bearing a bolt of a universal joint in an articulated yoke or an articulated-yoke half so as to form a running surface for the rolling elements of the axial bearing. The axial bearing thrust ring is machined on its surface which forms the running surface in such a manner that this surface has at least two surface regions which are formed or machined symmetrically with respect to an axis which extends radially through the theoretical center point of the annular element, in particular is an axis of symmetry of the thrust ring. The individual surface region extends substantially from the region of the axis of symmetry in the circumferential direction of the thrust ring. The surface is machined in such a manner that the cross-sectional area of the thrust ring in the machined region decreases as seen starting from the region of the axis of symmetry toward a second radially directed axis of symmetry on a line which is perpendicular to the first axis of symmetry. The thickness or width in the height direction of the thrust ring decreases in each case as seen from the inner circumference toward the outer circumference. As well as a first planar end side, the thrust ring also comprises a second end side, which has two surface regions which have been machined substantially symmetrically with respect to the first axis of symmetry SD of the thrust ring. Deviations caused by tolerances within a specific range are possible and are also to be included in the scope of protection. When the thrust ring is viewed from above, the first axis of symmetry runs in the radial direction through the theoretical center point and divides the thrust ring theoretically into two symmetrical ring segments. In terms of its profile in the circumferential direction as seen starting from the first axis of symmetry SD, in the circumferential direction, to a further, second axis of symmetry SSD which runs at right angles to the first axis of symmetry SD, each of the symmetrically machined surface regions can be described by a change in cross section of the thrust ring, which change is characterized by reductions in the thickness dimensions describing the cross-sectional area in the region of the inner circumference and the outer circumference of the thrust ring. The reductions in the thickness dimensions in the region of the inner circumference is less than in the region of the outer circumference, so that the surface is inclined from the inner circumference toward the outer circumference. This inclination has a specific gradient.
When integrated into a bearing system for bearing a bolt in an articulated yoke, the invention allows easy play adjustment, even in the loaded state, in the event of tilting of the elements which form the axial bearing races by constantly ensuring that the rolling elements bear with surface-to-surface contact against the corresponding running surface of the axial bearing, thus ensuring good load-bearing properties.
With regard to the design and/or arrangement of the machined surface regions, there are a plurality of options, which may differ in terms of the extent of the machined region in the circumferential direction and the form of the machined region from the inner circumference to the outer circumference of the thrust ring. In the former case, it is possible for the machining, starting from the axis of symmetry, to be carried out on both sides in each case at a specific distance from the axis of symmetry, i.e. for in each case only a segmental region of the thrust ring on both sides of the first axis of symmetry to be machined, starting at a specific circumferential distance from the first axis of symmetry. A further possibility is for the machining to be started directly at the first axis of symmetry. However, this is dependent on the specific application and the prevailing loads in that application and therefore the play adjustment which it is necessary to implement and the associated magnitude of the continuous change in cross section which is required. To simplify production, the cross-sectional areas at the first axis of symmetry SD and in the region of this axis are preferably characterized by identical thickness dimensions between inner circumference and outer circumference inclusive, i.e. the end sides of the thrust ring are parallel to one another in the region of the first axis of symmetry.
The change in the cross section of the thrust ring caused by a reduction in the thickness dimensions which describe the cross-sectional area, in order to avoid edge pressures in the radial direction, takes place, starting from the theoretical center point when the thrust ring is viewed from above, preferably directly from the inner circumference to the outer circumference of the thrust ring.
The changes in the thickness dimensions, which describe the change in cross section of the thrust ring, compared to the thickness dimension at the first axis of symmetry SD are, for relatively small and medium-sized joints, in the range of tenths of a millimeter. However, this is substantially dependent on the level of forces which occur in the bearing system of the cardan joint arrangement and, in particular, the level of the peripheral force and therefore the tilting of those elements of the axial bearing which form the race for the rolling elements which occurs. For large joints and high torques which are to be transmitted, thickness differences of up to 2 mm inclusive may be necessary. By way of example, the changes in the thickness dimensions which describe the change in cross section of the thrust ring at the inner circumference, between the first axis of symmetry SD and the second axis of symmetry SDS, which runs at right angles to the first axis of symmetry SD, are between 0 and 0.68 mm, and at the outer circumference are between 0 and 0.8 mm for an axial bearing of a certain size. The amount of material removed in the machined surface regions changes proportionally to the size of the axial bearing.
With regard to the design of the cross-sectional area, there are also numerous possibilities. In the unmachined state on the annular basic element, in the circumferential direction, this area is preferably characterized by a square or rectangular cross section. Other designs are conceivable, although it is necessary to take into account that at least that part of the surface of the thrust ring which theoretically forms a running surface should have a planar surface. The machining may take place in such a manner that the abrasion is carried out from the inner circumference to the outer circumference or the grinding tool acts on the surface in such a manner that abrasion in the region of the line perpendicular to the axis of symmetry takes place starting at a specific distance from the inner circumference, i.e. although a planar surface which is slightly inclined is formed in the region of the abrasion, the latter solution is only suitable for end sides to be machined which have different thickness regions between inner circumference and outer circumference, provided that the thickness of the thickness regions on the inner circumference and on the outer circumference is smaller than between these circumferences. Otherwise, shoulders will be formed, causing edge stresses.
The thrust ring is easy to manufacture, the material used is preferably heat treated case-hardened steels or other steels with an elasticity in the range from 180,000 N/mm2 to 230,000 N/mm2 inclusive. To simplify machining, it preferably has, as an annular basic element in the unmachined state, a cross section which is uniform in the circumferential direction. To produce the machined surface regions, the annular basic element is secured on both sides, in the region of its first axis of symmetry, with respect to a base surface. An element of specific height, preferably a piece of flat steel which is arranged and aligned in the region of the line which is perpendicular to the first axis of symmetry, is uniformly fitted under the annular element beforehand. This means that the region which can be described by the line perpendicular to the axis of symmetryxe2x80x94always with respect to the clamping of the thrust ring in the clamping devicexe2x80x94is enlarged. The annular basic element or the thrust ring is clamped in the region of the axis of symmetry with a specific, predefined force. This force is in turn dependent on the elasticity of the thrust ring and of the underfitted element and on the desired abrasion on that surface of the thrust ring which forms the running face, i.e. the surface regions which are to be machined. A grinding operation then takes place on both sides of the first axis of symmetry, the grinding tool being set for a specific amount of abrasion, and the difference in abrasion in the circumferential direction resulting only from the elastic deformation of the thrust ring. The abrasion in the circumferential direction of the thrust ring, as seen from above, and as seen in cross section from the inner circumference to the outer circumference of the thrust ring, is of different levels of magnitude. The grinding tool can act on the surface of the thrust ring in such a manner that the abrasion begins directly in the region of the axis of symmetry and extends over the region which can be described by the line which is perpendicular to the axis of symmetry on the thrust ring, in the circumferential direction, back toward the axis of symmetry. This means that the axis of symmetry can be used to divide the thrust ring into two theoretical ring segments, the perpendicular line further dividing the segments into two quadrants. The abrasion and therefore the machined surface regions on the surface of the thrust ring are configured in such a manner that they are formed symmetrically with respect to the first axis of symmetry. Therefore, a machined region extends substantially over a segment of the thrust ring which is in the form of half a ring.
In the most simple case, the device for machining the thrust ring comprises two clamping means which, in the region of the first axis of symmetry, secure the thrust ring with a specific, predefined force with respect to abase surface, and an underfitted means which is fitted beneath the thrust ring in the region of the line perpendicular to the axis of symmetry. In the most simple case, the clamping means may be screw connections, or alternatively a clamping device may be used.
The thrust ring for forming an axial bearing race may in this case be used in axial bearings for bearing systems for bearing universal joints in articulated yokes in cardan shafts of a very wide range of designs. Suitable designs of bearing systems are in particular those with
a) the axial bearing arranged in the region of the bolt root, or
b) the axial bearing arranged in the region of the end face of the bolt mounted in the articulated yoke, or
c) the axial bearing arranged in a bolt bore provided in the region of the end face of the bolt.
In both cases, the thrust ring forms in each case one running surface for the rolling elements of the axial bearing. In the first case, the thrust ring, as seen from the joint axis G toward the end face of the bolt mounted in the articulated yoke, forms the inner running ring for the rolling elements of the axial bearing, while in the second case the thrust ring forms the outer race.
In order to actually ensure play adjustment, it is necessary for the machined surface regions to be positioned in a fitted position as seen in the direction of rotation of the universal joint. The thrust ring is positioned in such a manner that the cross section which has the greatest change in thickness lies in a plane which can be described by the axes of the bolts mounted in the articulated yokes. For this purpose, means for positioning the machined surface regions in the fitted position in the axial bearing are preferably provided, these means being intended to prevent twisting out of this position. The means comprise either at least one projection arranged on the outer circumference or one of the end faces, which projection, in the fitted state, interacts with a recess provided on an element which forms the bearing surround, or at least one recess which is arranged on one of the end faces and, in the fitted state, interacts with a projection arranged on an element which forms the bearing surround.